I use a Speed Box II on my 1Xpression.  I had the Xpression for about a year before adding the Speed Box.  I didn't think it would do much and wouldn't have bought it if it weren't for the 30 day trial period I got.  It made a huge difference in my system.  It took my table to the next level or two.  After owning it for about 2 years or so, I unplugged it to see how it would sound without it.  It sounds awful in comparison.
I've heard a bunch of systems with outboard speed controllers.  Every one of them had a profound and positive impact, without exception.  I haven't heard the Speed Box and Speed Box SE side by side to say if its worth the extra money.  Most online places offer a 30 day return policy.  Maybe buy both and compare at home?  Music Direct carries them.  Not sure of where you are though.